Support for a stator of an electrical machine downstream of a turbine

Abstract

An electric machine is mounted at the rear of a turbine, and its stator (9) is mounted on a support (11) whose front end (10) is rigidly connected to the turbine housing and whose rear end, extending behind the stator (9), is connected to another fixed structure of the turbomachine, such as the rear cone (13), by a flexible linkage (49) allowing both radial and axial deflections, and damping. A more stable position of the stator (9) is thus obtained. (See Figure 2 for abbreviations.)

Description

Title of the invention: Supporting a stator of an electric machine downstream of a turbine

[0001] The subject of the invention is the support of the stator of an electric machine downstream of a turbine, at the rear end of an aircraft turbomachine.

[0002] The electrical machines in question here are electricity generators or reversible machines, which can also work as an electric motor and which are then capable of starting the turbine shaft or providing it with additional power. They complement the electricity generator usually found on the accessory gearbox (AGB) and which draws power, generally from the high-pressure body of conventional two-body turbomachines.

[0003] The turbine shaft is a shaft projecting from a casing at the rear end of the stator of the turbomachine, often called the turbine exhaust casing; this shaft preferentially drives the low-pressure spool of two-spool turbomachines. And the turbomachine can be a turbojet or a turboprop.

[0004] The addition of an electric machine to the rear of the turbine shaft proves to be quite easy and advantageous because the machine then occupies a volume which usually remains empty, and its rotor can be driven directly by the turbine shaft, sometimes even without a rotation speed change mechanism. A certain number of difficulties are however involved in such an arrangement.

[0005] Among these difficulties, it is necessary to mention the creation of a suitable support for the stator of the electric machine. It is in fact normal to mount this stator on a sleeve connected by a flange bolted to the exhaust casing of the turbine. The rigidity of this assembly may, however, prove insufficient when the sleeve is too long, and the overhang of the stator of the electric machine too great.

[0006] The object of the invention is therefore to improve the support offered by such a structure.

[0007] A general aspect of the invention is a turbomachine for an aircraft, comprising: a turbine shaft extending in an axial direction of the turbomachine to a rear end of the turbomachine; an electric machine comprising a rotor driven by the turbine shaft, and a stator supported by a support rigidly joined by a front end to a stator of the turbomachine; characterized in that the support is joined by a rear end, opposite the front end, to a structure rigidly joined to the turbomachine stator by a connecting piece comprising a sleeve sliding on the support in the axial direction, two coaxial rings, one of which is rigidly joined to the sleeve and the other to the structure, damping elements being arranged between the crowns.

[0008] It should be noted that these elements are of any number. We will often encounter a greater or lesser number of distinct elements distributed around the circumferences of the crowns, but a single element, continuous on these circumferences, would be possible.

[0009] Compared to the known assembly, the support sleeve is extended towards the rear so that its rear end is joined to the structure (and therefore to the stator of the turbomachine) by a flexible and damping connection, and so that the support is therefore supported by its two ends. The flexible nature of the connection makes it possible to overcome the disadvantages of relative movements between the exhaust casing and the shell and to avoid replacing the insufficient assembly with an overhang of the sleeve with an overly rigid, hyperstatic assembly. This avoids the appearance of excessive stresses during operation. The damping nature of the connection also makes it possible to avoid the appearance of excessive stresses, this time of a dynamic nature, during operation.

[0010] The damping elements can take many forms in concrete embodiments. They can thus extend in a radiating arrangement between the two crowns and consist, for example, of radiating springs, pairs of friction plates respectively subject to the crowns, or of compressible rings. Their deformable nature with moderate rigidity, elastic or not, ensures the support is held at its rear end.

[0011] According to a plausible construction, the support is cylindrical, the front and rear ends are circular, and the stator of the electric machine extends between the front end and the rear end.

[0012] According to other plausible constructions, the front end is bolted to an exhaust casing of the stator of the turbomachine, through which one end of the turbine shaft passes; and the structure is a tail cone ("plug") of the turbine.

[0013] Unlike usual designs where the support is mounted cantilevered by its front end only, it is generally advantageous here to make it quite flexible. For this purpose, it may include a more flexible portion between the front end and the stator of the electric machine.

[0014] The invention will now be described in its various aspects, characteristics and advantages by means of the following figures, which represent a preferred embodiment, given purely for illustrative purposes:

[0015] [Fig-1]: representation of an arrangement of known type comprising a machine electric at the rear of a turbine shaft;

[0016] [Fig.2]: representation of an embodiment of the invention;

[0017] [Fig.3]: a first embodiment of the damping elements;

[0018] [Fig.4]: a second embodiment of the damping elements;

[0019] [Fig.5]: a third embodiment of the damping elements;

[0020] [Fig.6]: a fourth embodiment of the damping elements;

[0021] [Fig.7]: a fifth embodiment of the damping elements;

[0022] [Fig.8]: a sixth embodiment of the damping elements;

[0023] [Fig.9]: complete diagram of a turbomachine where the invention is implemented.

[0024] We first refer to [Fig. 1]. It schematically and partially represents a turbomachine turbine, which comprises a turbine shaft 1 extending from front to rear in an axial direction XX of the turbomachine, rotating around a central axis thereof, and which is supported by various bearings 2, including a rear bearing 3 mounted in a stator 4 of the turbomachine. The turbine shaft 1 has a rear end 5, behind the rear bearing 3, projecting from an exhaust casing 6 which constitutes a rear face of the stator 4. An electrical machine 7 extends behind this exhaust casing 6, and it comprises a rotor 8 driven in rotation by the turbine shaft 1 while being mounted on its rear end 5, and a stator 9 mounted on a support 11 in the form of an approximately cylindrical sleeve, which is connected to the exhaust casing 6 by a bolted flange 10.

[0025] [Fig. 9] shows a complete turbomachine in which the device of [Fig. 1] is present. The turbomachine comprises, in addition to the turbine shaft 1 or low pressure shaft, a high pressure shaft 32 which surrounds it at a central portion in the axial direction XX. The bearings 2 for supporting the turbine shaft 1 and the high pressure shaft 32 are mounted in the stator 4 and the exhaust casing 6, as mentioned, as well as in a front casing 33 and an intermediate casing 34 located in front of the previous ones. The set of casings 4, 6, 33 and 34 forms an inter-vein casing 35. The turbomachine also comprises an outer casing 36 surrounding the inter-vein casing 35. A primary gas flow vein 37 extends inside the inter-vein casing 35, and a secondary vein 38 extends around the inter-vein casing 35 while being limited by the outer casing 36.A gas flow in the primary vein 37 and the secondary vein 38 is caused by a fan 39 at the front of the turbomachine, mounted on a fan shaft 40 extending in front of the turbine shaft 1 and coaxial with it to which it is connected by a speed reduction mechanism 4L. The primary vein 37 usually contains a low pressure compressor 42, a high pressure compressor 43, a combustion chamber 44, a high pressure turbine 45 and a low pressure turbine 46 from front to rear. A starter shaft 47 oriented approximately perpendicular to the axial direction XX is shown.

[0026] The general structure of this turbomachine is known. The invention could be applied to other turbomachine designs.

[0027] In many practical embodiments, the support 11 will have an im- bearing between the bolted flange 10 and the stator 9 and therefore an unacceptable overhang.

[0028] This is why, according to the invention represented in [Fig.2], the support 11 is extended by a front portion 12 in front of the stator 9 of the electric machine 7, which extends to the vicinity of a structure of the stator 4 of the turbomachine, like a rear cone ("plug") 13 of the turbine, which is also connected to the exhaust casing 6 by a bolted flange 14.

[0029] The front portion 12 of the support 11 is joined to the rear cone 13 by a flexible connection 49 whose characteristics are as follows. It firstly comprises a sliding portion 15 in the direction of the axis XX, composed of an inner sleeve 16 which belongs to the front portion 12, and an outer sleeve 17 belonging to a moving part 18 of the flexible connection 49. The outer sleeve 17 slides with reduced friction and reduced play around the inner sleeve 16 and therefore makes it possible to compensate for differential deformations, in particular expansions of thermal origin, between the rear cone 13 and the exhaust casing 4 during operation.

[0030] The moving part 18 also comprises a crown 19 concentric with the outer sleeve 17, and also concentric with a second crown 20 belonging to a fixed part 21 of the flexible connection 49; the fixed part 21 is fixed to the rear cone 13 by a flange 22 preferably bolted. Flexible and damping elements 23 are arranged between the crowns 19 and 20. They contribute to absorbing the misalignments between the support 11 and the rear cone 13, due to manufacturing inaccuracies or to static or dynamic forces. The mounting of the support 11 to the stator 4 of the turbomachine by its two ends is therefore not accompanied by excessive stresses either at rest or in service. The elements 23 are however provided with an elasticity or a resistance to deformations which maintains the support of the support 11 with a moderate force.

[0031] Certain embodiments of these flexible and damping elements 23 will now be described.

[0032] [Fig. 3] shows that these may be springs 24, here compressed between the rings 19 and 20 in the radial direction; for example, helical or leaf springs whose deformation is oriented radially. A certain number of them are distributed around the circumference, in a star-shaped arrangement. Such a device offers excellent flexibility and elasticity, and reduced damping. Different springs are conceivable. It would thus be possible to use a spring composed of undulations and going around the space between the rings 19 and 20.

[0033] [Fig. 4] shows that the elements 23 could consist of a pair of circular strips, pins or plates 25 and 26, one secured to the external ring 19 and the other to the internal ring 20, located face to face and rubbing against each other. Such a device offers both flexibility and significant cushioning.

[0034] Another design, shown in [Fig. 5], comprises deformable rings 27 whose cylindrical wall is compressed between the rings 19 and 20, and capable of being crushed at the points where these approach each other, the section of the rings 27 becoming elliptical. The rings 27 may be composed of turns of a cable wound in a helix. The deformation of the cable is accompanied by a dissipation of energy, and therefore damping.

[0035] [Fig. 6] shows an alternative embodiment, according to which elastic and damping pads 28 are interposed between the rings 19 and 20 in place of the ring or rings 27. The pads 28 can be distributed in any number around the circumference of the rings 19 and 20. The pads 28 could be replaced by a continuous ring extending over the entire circumference of the rings 19 and 20, with the same representation. It would be possible to envisage pads 28 or continuous rings having all kinds of sections, solid or hollow.

[0036] Other designs, shown in Figures 7 and 8, illustrate that the flexible connection 49 could be composed of columns 29 or 30 extending in the axial direction XX between the rings, here 19a and 20a, and 19b and 20b. These rings, to which the columns 29 and 30 are fixed by their ends, are here coaxial without being concentric, and they face each other in the axial direction XX. The columns 29 and 30 are distributed over the circumference of the rings 19a and 20a, or 19b and 20b. The embodiment of [Fig.7] shows that the columns 29 can be cylindrical with a circular section, of perfectly regular shape; whereas the columns 30 of [Fig.8] have a thinned central portion 31 to increase their flexibility. Their section is rectangular. Greater flexibility in one direction (radial or angular, as the case may be) is then obtained.

[0037] Many other embodiments of the elements 23 are obviously possible.

[0038] In all these embodiments, elements such as radial slides join the rings 19 and 20 together, so as to maintain them both in an invariable axial position relative to the rear cone 13. The sleeves 16 and 17 are covered with a non-stick coating which reduces the friction between them. Their contact surface area can be quite large, in order to reduce the contact pressure and thus extend the life of the device. The axial sliding zone could also be ensured by other means, such as by a succession of axial direction pins distributed around the circumference of the turbomachine and which would replace one of the two sleeves 16 and 17.

[0039] The support 11 is advantageously less rigid than in conventional assemblies where it is supported only by the front end, again in order to reduce the internal stresses in the assembly. This can be achieved by assigning a smaller thickness to a front portion 48 extending between the bolted flange 10 and the stator 9 of the electric machine 7.

Claims

Claims

1. A turbomachine for an aircraft comprising: a turbine shaft (1) extending in an axial direction (XX) of the turbomachine to a rear end of the turbomachine; an electric machine (7) comprising a rotor (8) driven by the turbine shaft, and a stator (9) supported by a support (11) rigidly connected by a front end to a stator (4) of the turbomachine; characterized in that the support (11) is joined by a rear end, opposite the front end, to a structure (13) rigidly joined to the turbomachine stator by a connecting piece (49) comprising a sleeve (17) sliding on the support (11) in the axial direction, two coaxial rings, one of which (19, 19a, 19b) is rigidly joined to the sleeve (17) and the other (20, 20a, 20b) to the structure, and flexible elements (23) arranged between the rings (19, 20).

2. Aircraft turbomachine according to claim 1, characterized in that the crowns are concentric and the flexible elements extend in a radiating arrangement between the two crowns.

3. Turbomachine for aircraft according to claim 2, characterized in that the flexible elements (23) are radiating springs (24).

4. Turbomachine for aircraft according to claim 2, characterized in that the flexible elements are pairs of friction plates (25, 26), respectively secured to the crowns.

5. Turbomachine for aircraft according to claim 2, characterized in that the flexible elements are compressible rings (27).

6. Aircraft turbomachine according to claim 1, characterized in that the flexible elements are columns (29, 30) extending in the axial direction (XX).

7. Aircraft turbomachine according to claim 6, characterized in that the columns (30) have a thinned, central part in the axial direction (31).

8. Turbomachine for aircraft according to claim 2, characterized in that the flexible elements comprise pads (28).

9. Turbomachine for aircraft according to claims 1 to 8, characterized in that the support (11) is cylindrical, the front and rear ends are circular, and the stator (9) of the electric machine extends between the front end and the rear end.

10. Turbomachine for aircraft according to claims 1 to 9, characterized in that the support comprises a more flexible portion (48) between the front end and the stator (9) of the electric machine.

11. Aircraft turbomachine according to claims 1 to 10, characterized in that the front end is bolted to an exhaust casing (6) of the stator of the turbomachine, through which one end (5) of the turbine shaft passes.

12. Aircraft turbomachine according to claims 1 to 11, characterized in that the structure (13) is a turbine rear cone.

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